Chuck posted a re-work in which he applied a channel from RGB to the Lightness layer of the LAB version of that image.

<edit> May have been the LAB layer, now I do not remember which

Aside from a new concept, the Image -> Apply Image command initially was kicking my butt until I took time to relax and carefully read the Help instructions. This way one achieves perfect registration and in effect, a perfect mask.

Lots more to learn and explore here...if one is interested in that sort of thing...and I must admit at the moment capturing images has taken a back seat to processing, at least for me.

There's a saying in woodworking that goes something like this (crude/rough):
"A great finisher (sanding/staining,etc.) can make an average woodworker look great ... an average finisher can make a great woodworker look average."

In my mind this translates to the "photographer" & "printer/lab" relationship ... to which we have become our own "lab" in this digital era.
Excellent processing (not funky photoshop tricks, fun as they are) is definitely the greatest area for gain, imo. Which is largely why all the new camera hype interests me so very little ... i.e. you still will need to be a good PP'er to extract the most out of your imagery.

The apply image trick is one I learned in the Dan Margulis "Photoshop for Professionals" book. He has a second on Lab processing which I have not read but understand is quite good.

RGB filters are used on a digital sensor because equal parts of RGB light create neutral gray tones, but RGB isn't very good at recording detail in objects with strong RGB or CYMK colors due to the way the color is split into the discrete channels by the filters over the sensor sites and how that process differs from the way the eye senses color.

RGB doesn't mimic the way the eyes perceive color. The cones in the eyes sense blue/yellow and green/magenta, not RGB. The rods in the eyes, which cover most of the retina, are sensitive to narrow band of greenish light and are 3000x more sensitive than the cones. The sensitivity difference limited spectral sensitivity of the rods is the reason why a Bayer RGB sensor needs twice as many green sensor sites as red and blue.

Photoshop and Lightroom use CIE*Lab as the "translation" space. Created back in the 1930s the Lab model of color is based on the gamut humans can see with their eyes based on how the cones and rods of the eye work. Luminance carries the detail similar to how the monochromatic rods record what hits the retina: as a B&W image. The a and b channels record the relative amounts of blue/yellow and magenta / green similar to how the cones of the eye actually sense color.

RAW files and JPGs are also encoded similarly as Luminance, blue/yellow, green/magenta components then decoded back into RGB to drive the RGB pixels on the monitor. When you open a RAW file in ACR or Lightroom and pick an editing space (sRGB, AdobeRGB, ProPhotoRGB) the discrete colors defined by the number of bits at capture are assigned both an absolute set of Lab coordinates based on the size of the editing Gamut.

To visualize how this mapping works create a file with solid blocks of RGB and CYMK then convert the file from sRGB, Abobe, ProPhoto. http://super.nova.org/TP/PrinterTestPatches_sRGB.jpg
The RGB values always stay the same and the blocks will look same on the screen, but if you open the color picker you'll see that the Lab values change.

In Photoshop you can switch image mode back and forth from RGB to Lab without affecting gamut because the Lab is the translation space. That's what allows Apply Image to overcome the limits of RGB capture in primary and secondary colors.

Yellow is R+G in equal amounts. In a bright yellow flower most of it will be almost fully saturated 240+ values of R and G, with darker shading recorded in the only remaining channel, B. The B "grays down" the R+G yellow. Magenta and Cyan objects are similar in that two channels carry the color leaving only one remaining to provide most of the clues about 3D shape and texture. Reds, blues an greens similar to the colors of the filters on the sensor can also lack detail but in those colors there are two other channels (e.g. G and B for Red) creating the shading.

Because there isn't much blue light reflecting off a yellow flower onto the sensor the camera does a pretty lousy job of recording the same amount of detail your eyes see in the flower. As a result a photo of Daffodils or Sunflowers always looks flat for a reason that isn't easily grasped — unless you know all that color theory stuff above, which I learned managing offset printing for a living

In an Lab copy of a Daffodil the detail is carried in the L channel as a B&W image. That detail can be enhanced in the flower by finding the channel in an RGB copy of the flower which has the most shading details (Blue) and adding it to the L channel of the Lab copy...

This is an unusual application of the technique but the only one I have on line which shows the Apply Image user interface:

The person I was helping in that case wanted to make the girl's freckles more prominent. Looking at the RGB channels the freckles were most prominent in the Blue channel because skin is predominantly R+G with B creating the darker shading. What the screenshot shows is how the detail in the Blue channel was copied into an Lab copy of the same file. Here are the steps if you want to try it:

1) Start by opening the file and saving two separate copies in .PSD format: Keep one in RGB, but before saving the other change the mode to Lab.

2) Open both copies. Make the Lab copy active and open the channel window.

3) Click on the L channel - that select it as the destination for the applied data.

4) Hold down the command key and press the tilde key ~ That will change the view on the screen from just the L channel to the entire color image, which allows you to see the effect of applied layer.

5) As shown in the screen shot select the channel with the detail in the RGB copy as the source. The target layer L was set in step 3. The mode menu controls how the Blue channel info is added to the L channel. Overlay adds the two numerical tonal values together. As shown in screen shot you need to adjust the % of the Blue that is applied by eye until you get a result you like. Also try different modes such as multiply.

6) Once you get the color to taste in the Lab file you convert it back to RGB.

In the case of a Daffodil doing the Apply image to add more detail to the yellow flower will also affect all the other content of the photo. So the next step is to mask out everything except the flower in the edited version. There are lots of ways to do that in Photoshop. I usually just select all in the edited Lab>RGB file, copy, then paste as a new layer in the other unchanged RGB copy creating a new layer on top. I then use the magic wand or selective color to isolate the flower and create the mask on the top layer.

Once the edited version of the flower is isolated with the mask its just a matter of adjusting the % opacity on the top layer to blend in the "detail on steroids" into the original. To nuance it even more selectively shade the mask on the edit layer.

One of the advantages of CS5 vs LR is the abilty to create layers and mask to apply corrections selectively. The masking tools in CS5 are also much improved over earlier versions of Photoshop.

The value of learning as many PhotoChops as possible is that it allows you to see past what your eyes are seeing to understand before you take a photo what the final image, with manipulation, can look like.

Working in printing I've used Photoshop since version 1 in the early 90's years before ever owning a digital camera. Its been part of my "creative DNA" (to the extent the son of an engineer and has any) as long as I've been shooting digital. Before digital, back in the days when I used the zone system and B&W film to manipulate reproduction, I also used yellow or red filters to darken sky, or a green filter to all more contrast and "pop" to foliage. I also don't recall ever making a print where I didn't also do some burning and dodging to alter the mid tones and guide the viewer to the focal point.

cgardner wrote:
The apply image trick is one I learned in the Dan Margulis "Photoshop for Professionals" book. He has a second on Lab processing which I have not read but understand is quite good.

I have BOTH of these books ... incredible amount to digest, and a bit technical for many readers. They seem a bit 'outdated' by today's newer crop of books due to his writing style, but the information is foundational & timeless, imo.

Dan ascribes to explain and develop understanding, rather than the mantra of "Do this, Do That, Slide here, Slide there, VOILA, you're done ... now you too can copy me ... thanks for your money ... please come back and by my next book since you really didn't learn much with this one." In other words, they're "old school" books ... no wonder I like them.

They serve as bulwarks to my library, now if I can just continue to put them in practice & practice & practice.

Dan and I come from similarl work backgrounds in the CYMK centric offset printing, starting in the 70s when color corrections where done by masking off a halftone with lacquer and chemically etching the dots to change their size. So I relate to his concepts very easily.

As for his approach? Everyone who teaches formally in a class or book does it from the lesson plan baseline of what they discovered by trial and error and cumulative experience and tries to present the information in a logical sequence of technical facts leading towards the understanding of a larger goal.

Books by their very nature are "old school". The Internet, Google and forums like this has changed the way people learn things like photography and the related skill sets of post processing and printing. Now people "cherry pick" nuggets of information on an ad hoc basis, which is more efficient in meeting the immediate need for information to solve an immediate problem but doesn't provide the context to understand why things work and solve a slightly different one next time.

The underlying goal of formal education isn't cramming minds full of facts, but rather teaching the students how to solve problems by connecting facts in a logical progression to arrive at the best strategy to solve problems and accomplish the goals. That's the part that is missing in education via Google and narrowly focused forum "How do I .... " questions.

The measure of the value of and information gained intellectually comes from validating it by personal experience and people of different temperaments do that differently. Tuition and "book learning" just eliminates much of the trial and error by giving the student a starting baseline of what is known to work best most of the time in a situation. That doesn't mean it will always work best or is the best solution for a different problem, but provides a blueprint baseline for comparing everything else.

I taught in a classroom on the college level for five years back in the late 70's using a lesson plan that led students up structured learning curve in a photo reproduction 101 which allowed them to understand the more advanced concepts in photo reproduction 201 the next semester. The main difference in learning styles I've observed between intuitive and sensing types is that an intuitive will come across new information and if it fits logically with what they already know will accept it on face value as valid without actually trying it and seeing the cause and effect themselves.

I discovered back in the mid-90s when starting to give photo advice on the net that if I using that traditional "Do this it works." approach I'd get a lot of "there are no rules" blowback Trolls from people high on the learning curve who learned by trial and error rather than by formal tuition. That's rule rather than the exception in photograph nowadays.

Over the course of several years and hundreds of C&Cs and edits I realized that in the Internet age people learn best from their personal baselines. On the net people asking specific questions usually have some level of understanding of the topic. Unfortunately often their understanding based on incorrect assumptions about the underlying cause and effect. People who are convinced they know how something works based on incorrect assumptions are the most difficult to teach because first they demand you prove their assumptions are wrong before opening their minds to the possibility of alternate, more technically sound approaches you offer are more effective.

The use of fill is a good example. It seems logical to put fill on the side opposite the key light because that's where the shadows are seen, but on a cause and effect level its not a good strategy because the fill will create shadows and dark voids in the lighting pattern which on a face are very distracting, "hard" looking and unflattering. It also puts the side of the nose furthest from the fill which makes its shadow the darkest and most distracting one on the face.

Placing fill over the camera seems at first glance to be a very bad idea because most people start from a baseline of flash on or over the camera and see that it sucks. But once the person tries it and grasps the cause and effect of fill shadows = hard harsh lighting the logic of placing fill over the camera makes sense compared to everything else they try.

When I C&C a portait one of the first things I notice is the tone of the nose shadow vs. all the other shadows on the face. Shadows provide the clues to 3D shape and a dark nose shadow draws attention to the nose and if not skillfully places via the key light angle exaggerates its shape. So just from that one clue I can tell a lot about key and fill placement and see ways to make it more effective compared to my experience using centered even fill.

But curiously some, including many pros, have such a strong belief based on personal experience that any light near the camera is "bad" lighting they will never even try the idea and see if it works. Others trying the idea will see no problem with having shaded fill and dark distracting nose shadows on the portraits they take and will continue putting fill on the side and shading it. In the end what matters is something works for you. The best a teacher or author can do is convey what has worked for them in the hope someone will actually try it and find it easier and more effective at solving the problem.

Comparison is the key to both validation of new ideas and understanding how they work.

I like it when people post several portraits of the same subject with different facial angles and lighting patterns. It makes it easy for me to point out how photo #1 has a more flattering angle than #2 or that how the lighting in #3 is better because its not spilling past the eye notch and hitting ear as in #4 taking in the same light but with the face turned into slightly differently. People will grasp the difference and validate the advice as being valuable much more readily by seeing the differences by comparison on a conscious intellectual level than if you simply told them to keep the key light 45° from the nose. Once they know the implications of having a nose shadow being the darkest shadow on the face intellectually and accept its not a good thing for flattering a face, it becomes part of their photographic baseline of what looks "normal".

That's one of the reasons I hang out here vs. spending the time writing book, and why I put an e-mail link on the bottom of every tutorial.

The way I learned the "proper" placement of fill was to lightly fill in the shadows from the POV of the viewer (aka camera position). Unless I am doing something special, this is my best starting place.

Yup ... "old school" does not provide 'instant gratification' that so many have become conditioned toward. I like a good tip, trick, here's how as well as the next person, but I do try to garner an understanding of what / why the tip, trick or method is working. Of course, that requires both more explanation on the part of the information giver, and more study on the part of the information receiver.

It isn't always necessary to understand, sometimes being shown can be sufficient to start with. Nice to have people around FM that are capable of both.